FR-A-2 582 058 for example already discloses hydraulic mechanisms comprising a cam; a cylinder-block mounted to rotate with respect to the cam; a plurality of cylinders arranged in this cylinder-block; a plurality of pistons each mounted to slide inside a cylinder along an axis of slide of piston; a plurality of rollers for abutment of the pistons on the cam, each roller being mounted on a piston, rotating about a roller axis perpendicular to the axis of said piston by means of a bearing of rotation, being axially defined by two transverse faces, and being capable of penetrating, at least partially, inside the cylinder in which this piston is slidably mounted, the end of the piston in which is formed the bearing
for rotation of the roller, comprising two recesses each corresponding at least to the space included between at least the cylindrical surface of the roller, the surface of the cylinder and one of the transverse faces of the roller, said space being open in the upper part of the piston at least in the zone where the cylindrical surface of the roller projects from the piston; and two pieces for wedging each roller, which are each disposed in one of said two recesses between the corresponding end of the roller and the inner face of the cylinder on which said wedging piece abuts, in order to ensure axial holding of the roller in position parallel to its axis of rotation.
The means for holding in position the rollers supported by the pistons, known by FR-A-2 582 058, are efficient, but require machinings which increase the cost price of the mechanism. Moreover, in order to obtain failure-free operation, the means for holding these known mechanisms must be mounted with precision which, again, tends to increase the cost of said assembly.
It is a principal object of the invention to reduce these machining and assembly costs, by reducing the number of necessary machinings and even eliminating certain, and by reducing and eliminating certain prior precision assemblies.
To that end, the invention provides an arrangement whereby, along the axis of the piston, at least one of the two wedging pieces extends up to the lower part of the recess, so as, in the sense of extension of the piston out of the cylinder, to be displaced with said piston.
The following advantageous arrangements are, in addition, preferably adopted:
that part of the wedging piece opposite the end of the roller is defined by a cylindrical face which is in abutment on the inner face of the cylinder; PA1 the wedging piece is introduced in the corresponding recess without being fixed to any piece, in particular either to the piston or to the cylinder; PA1 or, in a variant embodiment, the mechanism comprises a device for maintaining the orientation of the piston with respect to the cylinder; PA1 this device for maintaining the orientation of the piston with respect to the cylinder is constituted by a groove, with which the wedging piece is provided, which extends parallel to the axis of the piston, which opens out in that face of this wedging piece opposite the corresponding end of the roller, and by a catch, which is fixed with respect to the cylinder vis-a-vis rotation about the axis of the piston and which is introduced, in said groove, so as to leave free the translation of said wedging piece with respect to the cylinder parallel to the axis of the piston; PA1 the device for maintaining the orientation of the piston with respect to the cylinder comprises a clip having an arm constituting said catch and disposed in the upper part of the cylinder-block, being hooked to an edge of the outer part of said cylinder-block; PA1 in a variant embodiment, the device for maintaining the orientation of the piston with respect to the cylinder is constituted by one of the two wedging pieces in the form of a support, which is fixed with respect to the cylinder, of an abutment face for limiting slide of the roller parallel to its axis; PA1 this wedging piece in the form of a support is advantageously constituted by a lunule rendered fast with the cylinder-block; PA1 at least certain of the wedging pieces disposed on at least one side of the transverse plane containing the axes of a plurality of pistons are each provided with a catch projecting opposite the abutment face of the roller and on which an elastic return device may be hooked, in order to allow the pistons to return in the cylinders until the rollers are brought out of abutment with the cam in a so-called "releasing" configuration of the mechanism; PA1 at least one of said wedging pieces which extends substantially to the lower part of the recess, extends in addition to that part of the cylindrical surface of the roller which projects out of the piston, being included between these two limits, so as, in the sense of the return of the piston in the cylinder, to be pushed by the cam itself towards the inside of the cylinder; PA1 in a variant embodiment, the roller is mounted in a bearing for rotation formed in the piston and projects axially beyond said bearing, of which the lower part is disposed at a level higher than that of the lower part of the corresponding recess of the piston, with the result that a housing is formed between the lower part of the recess and the end of the roller which projects axially beyond the bearing, whilst the lower part of the wedging piece presents, towards the corresponding end of the roller, a protuberance contained in said housing, so that the return displacement of the piston in the cylinder provokes a concomitant displacement of said wedging piece with respect to the cylinder; PA1 the lower part of the recess coincides with the lower part of the bearing for rotating assembly of the roller.
The advantages offered by the invention are in connection with the fact that, in its most simple form, the device for axially holding a roller requires no machining of the cylinder-block, since it is constituted by two wedging pieces not fixed on the cylinder-block, either in translation in the direction of slide of the corresponding piston, or in rotation about the axis of the corresponding cylinder. In the event of rotation about the axis of the cylinder not being free, preferred arrangements are proposed which also avoid any important machining and/or precision of the cylinder-block. The principal advantage obtained resides in the reduction of the number of machinings and, especially, in the reduction or elimination of the machining of a cumbersome, heavy and expensive item, the cylinder-block. The reduction of the cost price of the mechanism corresponds to this reduction in the machinings obtained by adopting the invention.